From 6d4a345d693bdcb1fc5b1ff9845eee8fb5d8b547 Mon Sep 17 00:00:00 2001
From: Brent <67750428+eggpeat@users.noreply.github.com>
Date: Thu, 23 Jul 2026 16:51:08 +0000
Subject: [PATCH] fix(coding-agent): defer ACP reserve confirmation

---
 packages/coding-agent/src/main.ts             |  4 +-
 packages/coding-agent/src/sdk.ts              |  7 +++-
 .../test/acp-lazy-startup.test.ts             |  6 +++
 .../test/sdk-model-selection.test.ts          | 37 +++++++++++++++++++
 4 files changed, 52 insertions(+), 2 deletions(-)

diff --git a/packages/coding-agent/src/main.ts b/packages/coding-agent/src/main.ts
index 65887bc08..db8278447 100644
--- a/packages/coding-agent/src/main.ts
+++ b/packages/coding-agent/src/main.ts
@@ -391,7 +391,9 @@ export function createAcpSessionFactory(args: AcpSessionFactoryOptions): AcpSess
 			authStorage: args.authStorage,
 			modelRegistry: args.modelRegistry,
 			agentId,
-			hasUI: false,
+			// Preserve reserve-policy confirmation until ACP capabilities are known
+			// without enabling AskTool or other UI-only session behavior.
+			deferUsageReserveConfirmation: true,
 			enableMCP: false,
 			titleSystemPrompt,
 		});
diff --git a/packages/coding-agent/src/sdk.ts b/packages/coding-agent/src/sdk.ts
index 8d81f6653..8284ace4b 100644
--- a/packages/coding-agent/src/sdk.ts
+++ b/packages/coding-agent/src/sdk.ts
@@ -520,6 +520,11 @@ export interface CreateAgentSessionOptions {
 
 	/** Whether UI is available (enables interactive tools like ask). Default: false */
 	hasUI?: boolean;
+	/**
+	 * Defer `confirm` reserve-policy fallback until AgentSession prompt-time UI is configured.
+	 * ACP uses this while capabilities are negotiated without enabling UI-only tools.
+	 */
+	deferUsageReserveConfirmation?: boolean;
 
 	/**
 	 * Opt-in OpenTelemetry instrumentation forwarded to the underlying Agent.
@@ -2205,7 +2210,7 @@ export async function createAgentSession(options: CreateAgentSessionOptions = {}
 								`Usage reserve reached for ${primary.model.provider}/${primary.model.id}; reserve policy is fail-closed.`,
 							);
 						}
-						if (usageReservePolicy === "auto" || !options.hasUI) {
+						if (usageReservePolicy === "auto" || (!options.hasUI && !options.deferUsageReserveConfirmation)) {
 							usageFallbackTriggered = true;
 							continue;
 						}
diff --git a/packages/coding-agent/test/acp-lazy-startup.test.ts b/packages/coding-agent/test/acp-lazy-startup.test.ts
index 3f9f3cc75..eb855020c 100644
--- a/packages/coding-agent/test/acp-lazy-startup.test.ts
+++ b/packages/coding-agent/test/acp-lazy-startup.test.ts
@@ -492,6 +492,8 @@ describe("ACP lazy startup", () => {
 			const { runRootCommand } = await import("@oh-my-pi/pi-coding-agent/main");
 			const { createAgentSession } = await import("@oh-my-pi/pi-coding-agent/sdk");
 			let session: AgentSession | undefined;
+			let sessionHasUI: boolean | undefined;
+			let deferredUsageReserveConfirmation: boolean | undefined;
 
 			const stopped = runRootCommand(
 				{
@@ -514,6 +516,8 @@ describe("ACP lazy startup", () => {
 					discoverAuthStorage: async () => authStorage,
 					createAgentSession: options => {
 						const sessionOptions = options ?? {};
+						sessionHasUI = sessionOptions.hasUI;
+						deferredUsageReserveConfirmation = sessionOptions.deferUsageReserveConfirmation;
 						return createAgentSession({
 							...sessionOptions,
 							workspaceTree: sessionOptions.workspaceTree ?? emptyWorkspaceTree(sessionOptions.cwd ?? cwd),
@@ -533,6 +537,8 @@ describe("ACP lazy startup", () => {
 			}
 			expect(session.model.provider).toBe("runtime-provider");
 			expect(await session.modelRegistry.getApiKey(session.model)).toBe("cli-runtime-key");
+			expect(sessionHasUI).toBe(false);
+			expect(deferredUsageReserveConfirmation).toBe(true);
 			await session.dispose();
 		} finally {
 			authStorage.close();
diff --git a/packages/coding-agent/test/sdk-model-selection.test.ts b/packages/coding-agent/test/sdk-model-selection.test.ts
index 682a2649b..67549e7c8 100644
--- a/packages/coding-agent/test/sdk-model-selection.test.ts
+++ b/packages/coding-agent/test/sdk-model-selection.test.ts
@@ -459,6 +459,43 @@ describe("createAgentSession deferred model pattern resolution", () => {
 		}
 	});
 
+	test("defers ACP reserve fallback until prompt-time capabilities are configured", async () => {
+		const settings = Settings.isolated({
+			"retry.usageAwareFallback": true,
+			"retry.usageReservePolicy": "confirm",
+		});
+		settings.setModelRole("task", "runtime-provider/runtime-model,runtime-provider/runtime-reasoning-model");
+		const options = await buildSessionOptions("task");
+		vi.spyOn(options.authStorage, "getModelUsageHealth").mockImplementation(async (_provider, healthOptions) =>
+			healthOptions.modelId === "runtime-model"
+				? {
+						state: "reserve",
+						accounts: [
+							{
+								credentialId: 1,
+								credentialType: "oauth",
+								state: "reserve",
+								remainingFraction: 0.05,
+							},
+						],
+					}
+				: { state: "healthy", accounts: [{ credentialId: 2, credentialType: "oauth", state: "healthy" }] },
+		);
+		const { session } = await createAgentSession({
+			...options,
+			modelPatternFallbackRole: "subagent:usage-aware-acp",
+			settings,
+			hasUI: false,
+			deferUsageReserveConfirmation: true,
+		});
+		try {
+			expect(session.model?.provider).toBe("runtime-provider");
+			expect(session.model?.id).toBe("runtime-model");
+		} finally {
+			await session.dispose();
+		}
+	});
+
 	test("enforces fail-closed reserve policy without requiring a fallback candidate", async () => {
 		const settings = Settings.isolated({
 			"retry.usageAwareFallback": true,